Double-Sided Starter/Generator for Aircrafts

ABSTRACT

An electromagnetic machine for extracting power from a turbine engine includes an outer rotor and an inner rotor rotatably supported adjacent to a stator. The stator is disposed between the inner and outer rotors. The stator has an inner set of windings disposed on an inner surface adjacent to the inner rotor, and an outer set of windings on an outer surface of the stator adjacent to the outer rotor. A plurality of permanent magnets are disposed on an inner surface of the outer rotor element and on an outer surface of the inner rotor element. Air gaps are defined between the outer surface of the stator and the outer permanent magnets, and between the inner surface of the stator portion and the inner permanent magnets. The inner stator windings form a set of multiple-phase windings. and the outer stator windings form a set of multiple-phase windings.

FIELD OF THE INVENTION

The present invention is directed to an electrical machine foraircrafts, and more particularly to an electrical motor/generator havingcoaxial dual rotors independently driven by a high- and low-pressureturbine shaft, respectively, of a gas turbine engine.

BACKGROUND OF THE INVENTION

A gas turbine engine generally includes one or more compressors followedin turn by a combustor and high and low pressure turbines. These enginecomponents are arranged in serial flow communication and disposed abouta longitudinal axis centerline of the engine within an annular outercasing. The compressors are driven by the respective turbines andcompressor air during operation. The compressor air is mixed with fueland ignited in the combustor for generating hot combustion gases. Thecombustion gases flow through the high and low pressure turbines, whichextract the energy generated by the hot combustion gases for driving thecompressors, and for producing auxiliary output power.

The engine power is transferred either as shaft power or thrust forpowering an aircraft in flight. For example, in other rotatable loads,such as a fan rotor in a by-pass turbofan engine, or propellers in a gasturbine propeller engine, power is extracted from the high and lowpressure turbines for driving the respective fan rotor and thepropellers.

It is well understood that individual components of turbofan engines, inoperation, require different power parameters. For example, the fanrotational speed is limited to a degree by the tip velocity and, sincethe fan diameter is very large, rotational speed must be very low. Thecore compressor, on the other hand, because of its much smaller tipdiameter, can be driven at a higher rotational speed. Therefore,separate high and low turbines with independent power transmittingdevices are necessary for the fan and core compressor in aircraft gasturbine engines. Furthermore since a turbine is most efficient at higherrotational speeds, the lower speed turbine driving the fan requiresadditional stages to extract the necessary power.

Many new aircraft systems are designed to accommodate electrical loadsthat are greater than those on current aircraft systems. The electricalsystem specifications of commercial airliner designs currently beingdeveloped may demand up to twice the electrical power of currentcommercial airliners. This increased electrical power demand must bederived from mechanical power extracted from the engines that power theaircraft. When operating an aircraft engine at relatively low powerlevels, e.g., while idly descending from altitude, extracting thisadditional electrical power from the engine mechanical power may reducethe ability to operate the engine properly.

Traditionally, electrical power is extracted from the high-pressure (HP)engine spool in a gas turbine engine. The relatively high operatingspeed of the HP engine spool makes it an ideal source of mechanicalpower to drive the electrical generators connected to the engine.However, it is desirable to draw power from additional sources withinthe engine, rather than rely solely on the HP engine spool to drive theelectrical generators. The LP engine spool provides an alternate sourceof power transfer, however, the relatively lower speed of the LP enginespool typically requires the use of a gearbox, as slow-speed electricalgenerators are often larger than similarly rated electrical generatorsoperating at higher speeds. The boost cavity of gas turbine engines hasavailable space that is capable of housing an inside out electricgenerator, however, the boost section rotates at the speed of the LPengine spool.

However, extracting this additional mechanical power from an engine whenit is operating at relatively low power levels (e.g., at or near idledescending from altitude, low power for taxi, etc.) may lead to reducedengine operability. Traditionally, this power is extracted from thehigh-pressure (HP) engine spool. Its relatively high operating speedmakes it an ideal source for mechanical power to drive electricalgenerators that are attached to the engine. However, it is desirable attimes to increase the amount of power that is available on this spool,by transferring torque and power to it via some other means.

Another source of power within the engine is the low-pressure (LP)spool, which typically operates at speeds much slower than the HP spool,and over a relatively wider speed range. Tapping this low-speedmechanical power source without transformation result in impracticallylarge generators.

Many solutions to this transformation are possible, including varioustypes of conventional transmissions, mechanical gearing, andelectromechanical configurations.

One solution is a turbine engine that utilizes a third,intermediate-pressure (IP) spool to drive a generator independently.However, this third spool is also required at times to couple to the HPspool. The means used to couple the IP and HP spools are mechanicalclutch or viscous-type coupling mechanisms.

U.S. patent No. U.S. Pat. No. 6,895,741, issued May 24, 2005, andentitled “Differential Geared Turbine Engine with Torque ModulationCapacity”, discloses a mechanically geared engine having three shafts.The fan, compressor, and turbine shafts are mechanically coupled byapplying additional epicyclic gear arrangements. The effective gearratio is variable through the use of electromagnetic machines and powerconversion equipment.

U.S. Pat. No. 6,924,574 discloses a dual-rotor, radial-flux,toroidally-wound, permanent-magnet machine having improved electricalmachine torque density and efficiency. At least one concentricsurface-mounted permanent magnet dual-rotor is located inside andoutside of a torus-shaped stator with back-to-back windings,respectively. The permanent magnet machine includes at least onepermanent magnet rotor having a generally cylindrical shape with aninner rotor component and an outer rotor component, and at least onestator having a hollow cylindrical shape positioned within an openingbetween the inner and outer components of the permanent magnet rotor. Aplurality of polyphase windings of electrical wires are wound around theat least one stator.

Therefore, there is a need for a gas turbine engine with a compactmotor/generator that is capable of generating electric power from boththe LP and HP engine spools.

SUMMARY OF THE INVENTION

The present invention is directed to a double-sided dual-shaft (DSDS)electrical machine having a rotor connected to the HP spool and a rotorconnected to the LP spool. A stator portion is disposed between the tworotors. The DSDS electrical machine is configured to generate electricpower from either or both rotors. The inner and outer rotor shafts ofthe DSDS machine are independently driven by HP and LP shafts,respectively. The independent rotor shafts permit each rotor to rotateat different speeds, and to operate one side of the machine as agenerator, and the opposing side of the electrical machine as a motor,using power electronic converters. The stator includes a pair ofopposing windings. Each opposing set of stator windings is adjacent to arespective rotor, and separated from the associated rotor by an air gap.Thus, the speed and the direction of rotation of each rotor shaft isindependent of the other.

An advantage of the present invention is that both the HP and LP spoolscan be connected to the single compact generator having less mass andvolume compared to two separate electric machines.

Another advantage is that electrical power can be drawn form either orboth sides of the motor/generator.

A further advantage of the present invention is that it incorporates allfeatures from a double-sided structure motor/generator, includingreduced radial force on the stator, reduced stator yoke thickness,reduced frame mass and lower cost of construction.

Yet another advantage of the present invention is that partial load canbe sustained during some fault conditions, providing greaterreliability.

Another advantage is that HP and LP generator sections may beindividually optimized for speed range and power output in relation tonumber of poles.

Another advantage of the present invention is greatly reduced cost byproviding the capability of using a larger power rating machine insteadof two smaller machines, consuming smaller volume on the aircraft andmaking direct drive possible for some applications.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view schematic illustration of anexemplary aircraft turbofan gas turbine engine.

FIG. 2 is a partial axial cross-sectional view of the double-sidedelectrical machine of the present invention.

FIG. 3 is a partial cross-sectional view of the double-sided electricalmachine of the present invention.

FIG. 4 is a partial cross-sectional schematic illustration of thedouble-sided electrical machine of the present invention with differentnumber of phases for inner and outer portions.

FIG. 5 is a schematic representation of one exemplary interconnectionbetween the double-sided machine and power converter.

FIG. 6 is a schematic representation of another exemplaryinterconnection between the double-sided machine and power converter.

FIG. 7 is a schematic representation of a double-sided electric machineof the present invention connected to Low Pressure and High Pressurespools.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in FIG. 1 is an exemplary turbofan engine 10 having agenerally axially extending axis or centerline 12 generally extending ina forward direction 14 and an aft direction 16. The bypass turbofanengine 10 includes a core engine 18 (also called a gas generator) whichincludes a high pressure compressor 20, a combustor 22, and a highpressure turbine (HPT) 23 having a row of high pressure turbine blades24, all arranged in a serial, axial flow relationship. High-pressurecompressor blades 64 of the high-pressure compressor 20 are fixedlyconnected in driving engagement to the high pressure turbine blades 24by a larger-diameter annular core engine shaft 26 which is disposedcoaxially about the centerline 12 of the engine 10 forming a highpressure spool 21.

A combustor 22 in the core engine 18 mixes pressurized air from thehigh-pressure compressor 20 with fuel and ignites the resulting fuel andair mixture to produce combustion gases. Some work is extracted fromthese gases by the high-pressure turbine blades 24 which drives the highpressure compressor 20. The combustion gases are discharged from thecore engine 18 into a power turbine or low-pressure turbine (LPT) 27having a row of low pressure turbine blades 28. The low-pressure turbineblades 28 are fixedly attached to a smaller diameter annularlow-pressure shaft 30 which is disposed coaxially about the centerline12 of the engine 10 within the core engine shaft 26 forming a lowpressure spool 29. The low pressure shaft 30 rotates axiallyspaced-apart first and second stage fans 31 and 33 of an engine fansection 35. The first and second stage fans 31 and 33 include first andsecond stage rows of generally radially outwardly extending andcircumferentially spaced-apart first and second stage fan blades 32 and36, respectively.

A fan bypass duct 40 circumscribes the second stage fan 33 and the coreengine 18. Core discharge airflow 170 is discharged from the lowpressure turbine 27 to mix with a bypass airflow 178 discharged from thefan bypass duct 40 through a rear variable area bypass injector (VABI)53. Mixing takes place in a tail pipe 69 in which exhaust flow is formedwhich is discharged through a variable area exhaust nozzle. An optionalafterburner 130 may be used to increase the thrust potential of theengine 10.

Referring to FIG. 2, a double-sided, dual-shaft (DSDS) electric machineis generally designated as 100. The inner and outer rotors 72, 76, areindependent and rotatable at different velocity. Each rotor 72, 76 hasat least one bearing 73, 77 for each shaft 30, 26, respectively. Thebearing position and type may vary based on application requirements.

Referring next to FIGS. 2 and 3, the turbine engine 10 includes a DSDSmachine 100 comprising an outer rotor core 76 and an inner rotor core72, which are generally hollow cylindrical components with a statorportion 66 disposed concentrically between the inner and outer rotorcores 72, 76 about the axis 12. Opposing frame sections 56, 58 providerigid support for stator portion 66 inside the engine 10, and includecentral openings for bearings 73, 77, for rotatably supporting the LPshaft 30 and the HP shaft 26. An inner set of stator windings 67 aremounted on the radially inner surface of the stator portion 66. Innerstator windings 67 are interconnected to form a first set ofmultiple-phase windings 88 (see, e.g., FIGS. 5 & 6). An outer set ofstator windings 65 are mounted on the radially outer surface of thestator portion 66. Outer stator windings 65 are interconnected to form asecond set of multiple-phase windings 89 (see, e.g., FIGS. 5 & 6). Theouter rotor core 76 has outer permanent magnets 75 and an inner rotorcore 72 with inner permanent magnets 74. The stator portion 66 has outertooth portions 104 and inner tooth portions 106, which are separated byslots 80, 84. The outer stator windings or coils 65 and the inner statorwindings or coils 67 are retained in slots 80, 84, respectively by theouter stator coil retaining wedge 108 and inner stator coil retainingwedge 110. An outer air gap 62 is defined between the double-sidedstator portion 66 and the permanent magnets 75 attached to the outerrotor 76, and an inner air gap 64 is defined between the stator portion66 and the permanent magnets 74 attached to the inner rotor 72. In theembodiment, shown in FIG. 3, the stator portion 66 is structurallyreinforced through compression of a lamination stack by a plurality ofcircumferentially spaced bolts 68 arranged parallel with the axis 12 inthe stator yoke portion 116. The bolt shafts 70 and at least one boltend 68 are insulated from the laminations and frame structures byinsulator tubes 71 and insulator rings 79 to avoid induced electricalcurrents and resulting losses and heating. In the example shown in FIG.3, one bolt per slot is used and the bolthole positions are aligned withstator teeth 104, 106, e.g., with boltholes 69, however, more or lessbolts may be used, as will be appreciated by those skilled in the art.Also illustrated are air cavity 112 between outer stator windings 65 andthe air cavity 114 between the inner stator windings 67 for air-coolingthe windings 65, 67.

The stator windings 65, 67 disposed in the slots 80, 84 defined betweenpairs of tooth portions 104, 106, are arranged side-by-side in FIG. 3.The windings 65, 67 are preferably toroidally-wound around the statortooth portions 104, 106. These windings may also be arranged in top andbottom layers, or as a single coil per slot 80, 84. The inner coils 67are interconnected to form one set of multiple-phase windings, and theouter coils 65 are interconnected to form a second set of multiple-phasewindings. A converter 90 (see, e.g., FIGS. 5 and 6) is connected todrive each set of windings, respectively, so that each set of windingscan be operated independently. Therefore, in general, the HP and LPshafts 30, 26 can rotate concurrently in the same or in oppositedirections, and may be controlled for operation at matching velocity orat separate and distinct velocities.

The poles 74, 75 in this exemplary embodiment are surface-mountedpermanent magnet poles. Alternatively, interior permanent magnet poles,wound-field poles, reluctance rotor poles, cage or wound induction typepoles, etc. may be used in place of the permanent magnet poles foreither or both rotors 72, 76. The numbers of pole, slots, and phases forthe inner and outer machines may vary, depending on the particularelectrical power requirements. Further, the two sides can be configuredand optimized independently.

Reliability and fault tolerance is important for all electrical machinesused in an aircraft. According to the present invention, themultiple-phase windings from either the inner rotor portion 72 or theouter rotor portion 76 can be separated into multiple sets, wherein eachset of phase(s) is driven by an individual converter 90. Thus, in caseof failure of a converter 90 or a machine winding 65, 67, only one setof phase(s) is rendered inoperable, while the remaining phases remainoperable to provide power to the aircraft.

Referring to FIG. 4, an exemplary embodiment of the present inventionwhereby inner and outer stator windings 67, 65 are configured inindependent multi-phase generators. The outer set of windings 65 arearranged in six phases of multi-phase windings 65 designated as A₁through F₁. Permanent magnets 75 alternate in polarity between north (N)and south (S), which induce electromagnetic energy in windings A₁through F₁ as the magnets 75 are rotated on outer rotor 76 past thewindings A₁ through F₁ to form a magnetic flux path with the statortooth portions 104 across air gap 62. The inner stator tooth portions 67are arranged in this example into three phases of multi-phase windingsA₂ through C₂, which are independent of phase windings A₁ through F₁.Permanent magnet 74 provides the sole source of excitation of all threeof phase windings A₂ through C₂ associated with the inner statorwindings 67, as the magnets 74 are rotated on inner rotor 72 past thewindings A₂ through C₂ to form a magnetic flux path with the statortooth portions 106 across air gap 64.

Referring to FIGS. 5 & 6, each set of multiple-phase windings 88 aredriven by a converter 90, to permit each set of windings 88 to operateindependently of the other. Therefore, shafts 26, 30 can concurrentlyrotate (a) in opposite directions, (b) in the same direction atdifferent velocity, or (c) in the same direction and at the samevelocity.

FIGS. 5 & 6 are exemplary implementations wherein multiple-phasewindings 88 are separated into multiple sets. In FIG. 5, there are twosets 88 of phase windings—a first set of phase windings 86 configuredwith N1 phases, and a second set of phase windings 89 configured with N2phases. Each phases winding set 86, 89 is driven by an individualconverter 90. In an alternate embodiment, shown in FIG. 6, 3-phasewindings 88 are each driven by individual, dedicated converter units 90.

FIG. 7 illustrates an embodiment of the double-sided electrical machine100 in an aircraft engine. The DSDS machine 100 is connected to both theLP spool 30 and HP spool 26, to generate electric power and, in someinstances, to start the HP spool 26. The LP spool 26 is connected to theinner rotor 72 through a gearbox 92. The gearbox 92 may be either amechanical gearbox or a magnetic gearbox. The outer rotor 76 isconnected to the HP spool 30 through another gearbox 94 that maylikewise be a mechanical or magnetic device. The DSDS machine 100 canextract mechanical power from either inner rotor 72 or the outer rotor76 into electric power as needed. The relative amount of electric powerextracted from the HP or LP turbines through either shaft 26, 30 isfully controllable through the converter 90 and the machine is designedaccordingly. The gearboxes 92, 94 on the both sides are optional, andeither or both gearboxes can be removed depending on the system designparameters. Also, depending on the torque level and maximum velocity ofthe DSDS machine 100, the HP shaft 30 may be connected to the innerrotor and the LP shaft 26 connected to the outer rotor.

While the double-sided machine has been generally described as twogenerator configurations, it will be appreciated by those practitionersskilled in the art of electric machines that the DSDS machine mayoperate as a starter motor for the turbine engine 10 by energizingeither set of inner or outer windings 65, 67, thus inducing rotation inone of the rotor portions 72, 76. Preferably, the rotor connected to theHP turbine shaft is used as a starting motor, although either rotor maybe operable as a starting motor to start the engine 10.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An electromagnetic machine for extracting electrical power from a gasturbine engine comprising: an outer rotor element and an inner rotorelement rotatably supported adjacent to a fixed stator portion, thestator portion disposed concentrically between the inner and outer rotorelements about a central axis; opposing frame portions connected at afirst end and a second end of the stator portion to support the statorportion within the engine; the stator portion having an inner set ofstator windings disposed on a radially inner surface of the statorportion adjacent to the inner rotor, and an outer set of stator windingsdisposed on a radially outer surface of the stator portion adjacent tothe outer rotor; a plurality of outer permanent magnets disposed on aninner surface of the outer rotor element and a plurality of innerpermanent magnets disposed on an outer surface of the inner rotorelement; an outer air gap defined between the outer surface of thestator portion and the outer permanent magnets, and an inner air gapdefined between the inner surface of the stator portion and the innerpermanent magnets; the inner stator windings electrically interconnectedto form a first set of multiple-phase windings and the outer statorwindings electrically interconnected to form a second set ofmultiple-phase windings for powering an electrical load.
 2. Theelectromagnetic machine of claim 1, wherein the stator windings disposedin slots defined between pairs of tooth portions
 3. The electromagneticmachine of claim 1, wherein the inner and outer stator windings arearranged side-by-side within the slots.
 4. The electromagnetic machineof claim 1, wherein the inner and outer stator windings aretoroidally-wound around the stator tooth portions.
 5. Theelectromagnetic machine of claim 1, wherein the inner and outer statorwindings are arranged at least one layer.
 6. The electromagnetic machineof claim 1, wherein the inner and outer stator windings are arranged onewinder to a slot.
 7. The electromagnetic machine of claim 1, wherein theinner stator windings are interconnected to form one set ofmultiple-phase windings, and the outer stator windings areinterconnected to form a second set of multiple-phase windings.
 8. Theelectromagnetic machine of claim 1, also comprising: a plurality ofconverters, each of the converters connected to a set of windings toindependently drive the associated phase winding.
 9. The electromagneticmachine of claim 1, wherein a driveshaft of the HP turbine and adriveshaft of the LP turbine are concurrently rotatable in the same orin opposite directions, and controllably operable at matching velocityor at separate and distinct velocities.
 10. The electromagnetic machineof claim 1, wherein the opposing frame portions include axial openingsat opposing ends of the machine, and at least two bearings for rotatablysupporting the LP shaft and the HP shaft connected to the inner andouter rotor elements.
 11. The electromagnetic machine of claim 1,wherein the stator portion includes a plurality of outer tooth portionsdefining a first set of slots therebetween, and a plurality of innertooth portions defining a second set of slots therebetween, the outerstator windings retentively positioned within the first set of slots andthe inner stator windings retentively positioned within the second setof slots.
 12. The electromagnetic machine of claim 1, wherein the statorportion further comprising a lamination stack structurally reinforcedthrough compression by a plurality of circumferentially spaced boltsarranged parallel with the axis in a yoke portion of the stator portion.13. The electromagnetic machine of claim 12, wherein the bolt shafts andat least one bolt end being insulated from the lamination stack andframe structures by a plurality of insulator tubes and insulator ringsto avoid induced electrical currents and resulting losses and heating.14. The electromagnetic machine of claim 1, also comprising an aircavity between outer stator windings and an air cavity between the innerstator windings for air-cooling the windings
 15. A gas turbine enginecomprising; a fan, a compressor, a high pressure turbine and a lowpressure turbine in serial flow communication, and an electrical machinearranged coaxially; the electrical machine comprising: a fixed statorelement, a first rotor element and a second rotor element, the first andsecond rotor elements independently rotatable with respect to the statorelement; the first rotor element mechanically connected with a shaft ofthe high pressure turbine, and the second rotor element being connectedwith a shaft of the low pressure turbine; the stator element having aninner and outer multiple-phase winding sets wound thereon, each of thewinding sets configured to generate separate power outputs or to receivea separate excitation power source, the inner and outer winding setsbeing mutually exclusive; wherein each of the first and second rotorelements are configured to generate electrical power throughelectromagnetic coupling with the stator element when driven by theassociated high or low pressure turbine shaft, or to electrically drivethe associated high or low pressure turbine shaft when excited by anexternal electrical power source.
 16. A dual sided, dual shaftelectrical machine comprising: a fixed stator element, a first rotorelement and a second rotor element, the first and second rotor elementsindependently rotatable with respect to the stator element; the firstrotor element mechanically connected with a shaft of a first turbine,and the second rotor element being connected with a shaft of the secondturbine; the stator element having an inner and outer multiple-phasewinding sets wound thereon, each of the winding sets configured togenerate separate power outputs or to receive a separate excitationpower source, the inner and outer winding sets being mutually exclusive;wherein each of the inner stator windings and the outer stator windingsare configured for independent multi-phase windings and each of theinner and outer rotors are concurrently driven by rotatable shafts ofthe first and second turbines, the rotatable shafts being mutuallyindependent.
 17. The electrical machine of claim 16, wherein theindependent first and second rotor shafts rotate the first and secondrotor elements, respectively, at different speeds, and wherein one ofthe first and second rotor elements operates as a generator and theother rotor element operates as a motor.
 18. The electrical machine ofclaim 16, wherein the stator element including a pair of opposingwindings, each opposing set of stator windings being adjacent to arespective rotor, and separated from the associated rotor by an air gap,wherein the speed and the direction of rotation of the each rotor shaftis independent of the other.